Glasses demonstrating relatively high transmission in the infrared region of the radiation spectrum are well known in the art. One rather large use of such glasses has been as elements in the construction of commercial detection systems based upon sensitivity to heat or infrared radiation.
U.S. Pat. No. 3,723,141 provides a brief review of the prior art directed to glass compositions asserted to exhibit good infrared transmission. In general, those prior art glasses had displayed good transmittances to wavelengths no longer than six microns and, commonly, no greater than five microns. The patent described glass compositions in the lead bismuthate system capable of transmitting substantial amounts of infrared radiation at wavelengths longer than six microns. Those glasses consisted essentially, expressed in terms of weight percent on the oxide basis, of
PbO: 10-75 PA1 Bi.sub.2 O.sub.3 : 10-85 PA1 PbO+Bi.sub.2 O.sub.3 : at least 60 PA1 BaO: 2-25 PA1 ZnO: 1-10 PA1 SiO.sub.2 +B.sub.2 O.sub.3 +P.sub.2 O.sub.5 : &lt;1 PA1 Bi.sub.2 O.sub.3 : 8-80 PA1 PbO: 0-57 PA1 CdO: 0-32 PA1 PbO+CdO: at least 5% PA1 Fe.sub.2 O.sub.3 : 5-32.5 PA1 PbO: 10-85 PA1 Ga.sub.2 O.sub.3 : 5-30 PA1 Bi.sub.2 O.sub.3 : up to 85
Optionally, up to 10% individually and up to 20% collectively of the following oxides may also be present: As.sub.2 O.sub.3, CaO, CdO, GeO.sub.2, HgO, Sb.sub.2 O.sub.3, SrO, TiO.sub.2, Tl.sub.2 O.sub.3, the alkali metal oxides, and the colorant or transition metal oxides. A drawing appended to the patent, wherein percent transmission is plotted against transmitting wavelengths, indicated a transmittance of at least 50% at a wavelength of 7.5 microns, but a rapid loss of transmission at longer wavelengths.
U.S. Pat. No. 3,837,868 is asserted to be an improvement upon the glasses of U.S. Pat. No. 3,723,141, wherein those latter glasses were stabilized to better avoid devitrification through the inclusion of Fe.sub.2 O.sub.3. Those glasses consisted essentially, expressed in terms of cation percent on the oxide basis, of
Optionally, up to 15% total of compatible glassmaking constituents may also be present including up to 7.5% BaO and/or ZnO, up to 5% GeO.sub.2, V.sub.2 O.sub.5, NiO, CoO, and other transition metal oxides, and up to 2% B.sub.2 O.sub.3 +SiO.sub.2.
Rather than repeating the reviews of prior art supplied in those patents, the full disclosures of those patents are explicitly incorporated herein by reference.